Method for preparing a pearlescent pigment by coating metal oxides on the synthesized mica

ABSTRACT

Disclosed is a method for preparing a pearlescent pigment by coating metal oxides on the synthesized mica, involving the steps of grinding the synthesized mica by agitating the mica with water in a water mixer to a particle size between 100 and 500 μm and separating the mica, dispersing the separated particles of the synthesized mica in water and adding acid thereto to adjust pH between 1 and 4, adding the metal oxide precursors and a basic aqueous solution thereto while maintaining said pH range until the desired color is attained, and thereby forming at least one hydrous metal oxide layer on the particles of the synthesized mica, and filtering, water-washing, drying and calcining the synthesized mica coated with the metal oxide layer. The method may further involve the step of further pulverizing the synthesized mica roughly ground in a water mixer by using a conventional wet pulverizer so that less than 100 μm of the synthesized mica may be used as a base material. The suitable surfactants can be used in a water mixer as well as a conventional wet pulverizer. The pearlescent pigment prepared according to the present invention has excellent luster and chroma, since a coating layer of metal oxides is smooth and the dispersibility of the particles is excellent.

TECHNICAL FIELD

[0001] The preset invention relates to a method for preparing apearlescent pigment, more specifically a method for preparing apearlescent pigment having excellent luster and chroma, comprisingcoating metal oxides such as titanium dioxide, iron oxide and the likeon the pulverized synthesized mica as a base material, characterized bymodifying a grinding method of synthesized mica to improve the surfaceproperty thereof and/or adding suitable surfactants to the pigment toimprove a dispersibility of the particles.

PRIOR ART

[0002] Since the origin era of mankind, they have sought various naturalor synthetic pigments or dyes to express their own beauty. Among them, apearlescent pigment has been widely used, because it has the inherentbeautiful color of its own contrary to other general pigments or dyes. Ageneral red pigment or dye expresses a red color in any visual angle. Onthe other hand, the pearlescent pigment expresses double or multiplecolors depending on visual angle on account of an angular difference,which occurs when a portion of light permeating the pearlescent pigmentis reflected and the other portion of light is refracted. Thisphenomenon is observed in a natural pearl, a fish scale, a clamshell, abird's feather, or butterfly's wing and the like. In the past, there wasused a guanine taken from the scales of fishes such as a herring and ahairtail in order to realize the pearlescent luster. However, sincethese natural resources cannot fulfil the demands of the pearlescentpigment, intensive studies on synthesis of pearlescent pigments havebeen in progress.

[0003] Representative examples of the synthesized pearlescent pigmentsinclude mica pigments coated with a lead carbonate, a BiOCl or titaniumdioxide (TiO₂), but the pigments based on Al₂O₃, SiO₂, glass flake andthe like have been recently developed. Especially, the most commerciallyand widely used pearlescent pigment is the mica pigment coated withtitanium dioxide which employs high refractivity of titanium dioxide. Asa base material such as mica is coated with metal oxides or mixturethereof having high refractive index in a form of single or multiplelayers, an interface between two-layered media having differentrefractive index permits a visible light to partially reflect andtransmit. As the light beams refracted or transmitted at the interfacerecombine constructively or destructively to enhance the intensity onlyfor a certain wavelengths, the color corresponding to such wavelengthsintensified at a reflective angle is observed. The said titaniumdioxide-coated mica is advantageous in that it is excellent inweatherproof property, chemical resistance and physical property, isable to show diverse colors depending on the kind of the coated metalcompound or dye and the coating thickness, and is able to control itsparticle size to accord a certain use by a grinding/separating process.In addition, the said pigment is also advantageous in that it is widelyapplied to automobile coating, cosmetics, wall paper, floor materials,plastic extrusion/injection, synthesized leather, printing ink, paintand the like. However, when natural mica is employed as a base material,there happens a problem that its final product has no uniform qualitydue to different iron contents, hardness, impurities and the like, andexpresses yellowish color.

[0004] To solve the said problems, a technology to use the synthesizedmica as a base material of the pearlescent pigment has been developed.However, when the synthesized mica is used to prepare a pearlescentpigment, the pearlescent pigment has to maintain the merit of thesynthesized mica itself as well as has to exhibit more excellent lusterand chroma than the natural mica-produced pigment. When a pearlescentpigment is prepared with a synthesized mica by a conventional wetpulverizing method as disclosed in U.S. Pat. No. 6,056,815, the lusterand chroma of the pearlescent pigment deteriorate since the mica isground by direct friction between the roller and the bottom surface toimpair the surface of the mica. In other words, when the surface of thesynthesized mica is not partially smooth and uniform, the level ofluster and chroma required for the pearlescent pigment cannot beattained because of light scattering. Further, when a metal oxidecoating is not intensely bound on a base material, luster or chroma isdeteriorated. For the reason, it is assumed that the heat generated byfriction transforms the interface of the base material to lead adeterioration of binding between metal oxide and base material, andresults in partially peeling the coating on account of external physicalforce.

[0005] U.S. Pat. No. 5,741,355 to Yamamoto et al discloses a pearlescentpigment wherein the average refractive index of the synthesized mica isnot more than 1.58, the surface of synthesized mica particles issmoothened and made flaky, the iron content in the synthetic mica is notmore than 1.0% by weight and a pearl parameter given by specific volumeand powder luster value of the synthesized mica is not less than 10. The'355 patent shows that fine powder of synthetic mica is added by atleast 1% or more to the melt of synthetic mica during synthesis bymelting of synthesized mica and is solidified and crystallized, suchcrystallized mass of synthetic mica is pulverized, or the meltedsubstance as taken out through the perforation of the shell iscrystallized in the heat insulating case and pulverized, in case thatthe synthetic mica is pulverized to particle size of 100 μm or smallerusing hammer mill, roll mill, ball mill, etc., addition of highviscosity medium makes the synthetic mica flaky and thereby smootheningthe surface of the mica. However, '355 patent has a problem that itrequires an additional process to obtain the particles of the syntheticmica in such shape as shown in the patent, and thereby makes the processcomplicate and economically disadvantageous.

[0006] In the preparation of the pearlescent pigment, it is alsorequired that the interface of base material should be activated so asto prevent the small particles of the synthesized mica from beingagglomerated to the large particles or each other and that the metaloxide should be adsorbed onto the synthesized mica in a smooth anduniform form. When the metal oxide is not adsorbed onto the interface ofbase material, but agglomerated each other, the surface of the finalproduct is rough or the metal oxide is not bound to the base materialand form particles by themselves, and thereby deteriorate the luster andchroma of the pigment.

[0007] The present inventors have fervently studied for solving saidproblems. As a result, they have found that the surface of thesynthesized mica is maintained smoothly enough for coating metal oxidesthereon in case that the synthesized mica is ground to a pulverizedpowder by a water mixer rather than a conventional wet grinding means.In addition, the present inventors have developed a pearlescent pigmenthaving an excellent luster and chroma by adding a suitable surfactant tothe dispersion of the ground synthesized mica to uniformly disperse thesynthesized mica particles and to uniformly adsorb the hydrous metaloxide onto the surface of the base material.

DISCLOSURE OF THE INVENTION

[0008] It is an object of the present invention to provide a pearlescentpigment having excellent luster and chroma or color saturation bykeeping the surface of the synthesized mica used as a base materialsmooth during the grinding step thereof.

[0009] It is another object of the present invention to provide apearlescent pigment in which superior dispersibility of particles can beobtained by adding surfactants prior to coating metal oxides on thesynthesized mica.

[0010] It is still another object of the present invention to provide apearlescent pigment, which is excellent in weatherproof, chemicalresistance and physical properties and is able to exhibit various colorsdepending on the species of metal oxides or coating thickness.

[0011] It is still another object of the present invention to provide apearlescent pigment prepared in accordance with the method of thepresent invention.

[0012] Said objects can be achieved according to the present inventionas explained hereinafter. The present invention will be explained indetail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above objects, and other features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the drawings, in which:

[0014]FIG. 1 is a cross sectional view of a water mixer having a pitchpaddle-typed agitator structure used for grinding the synthesized micaaccording to the present invention;

[0015]FIG. 2 is an electromicroscopic photograph showing the surface ofpearlescent pigment particles prepared in Example 4; and

[0016]FIGS. 3 and 4 are electromicroscopic photographs showing thesurface of pearlescent pigment particles wherein titanium dioxidecoating layer is formed on the synthesized mica ground by a conventionalwet pulverizer.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] In the first embodiment of the present invention, there providesa method for preparing the pearlescent pigments by coating metal oxideson the synthesized mica, comprising the steps of:

[0018] (1) grinding the synthesized mica by agitating the mica withwater in a water mixer to a particle size between 100 and 500 μm andseparating the mica;

[0019] (2) dispersing the separated particles of the synthesized mica inwater and adding acid thereto to adjust pH between 1 and 4

[0020] (3) adding the metal oxide precursors and the basic aqueoussolution to the dispersion while maintaining said pH range until thedesired color is attained, and thereby forming at least one hydrousmetal oxides layers on the particles of the synthesized mica; and

[0021] (4) filtering, water-washing, drying and calcining thesynthesized mica coated with the metal oxides layers.

[0022] Said method may comprises an additional step of furtherpulverizing the synthesized mica roughly ground in a water mixer in thestep (1) using a conventional wet pulverizer so that 100 μm or less ofthe synthesized mica may be used as a base material.

[0023] In the second embodiment of the present invention, there providesa method for preparing pearlescent pigments by coating metal oxides onthe synthesized mica, comprising the steps of:

[0024] (1) grinding the synthesized mica by agitating the mica withwater in a wet pulverizer to a particle size between 5 and 500 μm andseparating the mica;

[0025] (2) dispersing the separated particles of the synthesized mica inwater and adding 0.0001 to 1.0% by weight of cationic, anionic, nonionicor amphionic surfactant thereto;

[0026] (3) adding acid to the dispersion containing the surfactant toadjust pH between 1 and 4;

[0027] (4) adding the metal oxide precursors and the basic aqueoussolution thereto while maintaining said pH range until the desired coloris attained, and thereby forming at least one hydrous metal oxideslayers on the particles of the synthesized mica; and

[0028] (5) filtering, water-washing, drying and calcining thesynthesized mica coated with the metal oxides layers.

[0029] The pearlescent pigments prepared in accordance with the presentinvention have excellent luster and chroma or color saturation, becausethe synthesized mica mass produced by a conventional method is ground bya water mixer without damage of their surfaces, and a suitablesurfactant is added prior to the coating process of metal oxides thereonwhich is carried out separately or together with said grinding stepthereby the coated particles do not agglomerate each other and the metaloxides are uniformly adsorbed/bound on the surfaces of the synthesizedmica used as a base material.

[0030] In the present invention, the synthesized mica used as a basematerial for metal oxides layers is produced by a conventionalresistance melting method. Since the synthesized mica mass produced bythe above method have about 1 to 10 cm of particle size, furtherpulverization is carried out to obtain suitable particle sizes forgrinding in the water mixer.

[0031] According to the present invention, it is required that it shouldbe ground in a size of 5 to 500 μm to be used for preparing apearlescent pigment.

[0032]FIG. 1 is a cross sectional view showing a water mixer having apitched paddle-typed agitator, which is used for grinding thesynthesized mica in accordance with the present invention.

[0033] In grinding the synthesized mica, water and the synthesized micaare introduced in the water mixer in a weight ratio of 10:1 to 1:1,agitated at the revolution speed of 100 to 1000 rpm for 0.5 to 2 hoursto give particles of the synthesized mica, preferably in the form offlake, having particle size between 100 and 500 μm. The obtainedsynthesized mica is suitable for a base material of pearlescent pigment,because water serves as a buffer not to substantially impair the surfaceof the particles and easily soaks friction heat when the agitatorpaddles are collided with the particles of the synthesized mica in thewater mixer. A water mixer with pitched paddle-typed agitator ispreferably used. However, since it is substantially impossible to grindthe synthesized mica in a particle size of 100 μm or less with a watermixer, it may be additionally ground in a conventional wet pulverizer toobtain smaller particle size of about 5 to 100 μm. A preferable exampleof such a wet pulverizer is an edge runner mill, which grinds thesynthesized mica by a friction between a rotating roller and horizontaldisc. As above, double grinding can make the surfaces of the particlesmuch smoother compared with the single grinding using only conventionalwet pulverizer.

[0034] The particles of the pulverized mica are preferable subjected toseparation to give a narrow distribution of particle size, because theparticle size of pearlescent pigment prepared in the present inventionis altered depending on the use of the pigment, and the uniform particlesize enhances luster of the mica.

[0035] According to the present invention, the representative examplesof the metal oxide layer coated on the particles of the synthesized micaare titanium dioxide (TiO₂) layer, iron oxide (Fe₂O₃) layer, orcombination thereof. The layer mixed or combined with the ocher metaloxide, or the additional metal oxide layer on the titanium dioxide layerand/or iron oxide layer may be formed for the purpose of changing thecrystalline structure of a coating layer to improve luster, preventingdiscoloration or exhibiting more diverse colors. The examples of themetal oxides forming one layer together with the main metal oxides orthe additional layer include tin dioxide (SnO₂), zirconium dioxide(ZrO₂), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), magnesium oxide(MgO), manganese dioxide (MnO₂) and the mixture thereof. Especially, theemployment of tin dioxide has an advantage that the anatase structure oftitanium dioxide(TiO₂) coating layer is able to be changed to a rutilestructure by precoating the surface of the synthesized mica with a thinlayer of the hydrous tin dioxide (SnO2) as disclosed in U.S. Pat. Nos.4,038,099 and 4,086,100 to improve luster and weatherproof property. Itis preferable that other assistant metal oxides than tin dioxide formone coating layer together with a main metal oxide, or a mixture of themain metal oxide and tin dioxide.

[0036] According to the present invention, the contents of the coatinglayer may be preferably about 5 to 60% by weight depending on thedesired colors and luster, and for improving weatherproof property. Asthe thickness of the layer sets thicker, the colors of silver, gold,red, purple, blue and green exhibit in order. In case that multiplecoating layers are formed, for example, forming the second coating layerfollowing the first coating layer, the colors of silver, gold, red,purple, blue and green repeatedly exhibit in order. In addition to thisforming of multiple structures, the calcined pigments may be re-coatedwith the metal oxides such as chromium, zirconium, aluminum, or may betreated with silane in order to exhibit diverse colors or renderadditional weatherproof property. Even though forming the multi-coatinglayer, the whole content of the metal oxides coated on the synthesizedmica is preferably 5 to 80% by weight because too thick coating layer isliable to be peeled off the base material.

[0037] The method for preparing the pearlescent pigment is describedhereafter.

[0038] At first, it is preferable that the particles of the synthesizedmica are dispersed in water in an amount of about 5 to 15% by weight. Itis preferable to use the deionized water, if possible, to prevent thedisturbance of adsorption by ion. After raising the temperature of thedispersion of the synthesized mica particles to 60 to 100°C., theprecursor material of the metal oxides or the mixtures thereof are addedto the dispersion. For the precursor components of the metal oxidescoated according to the present invention, the examples of theprecursors of titanium dioxide are TiCl₄ (TiOCl₂ in an aqueoussolution), TiOSO₄ etc., and the examples of the precursors of iron oxideare FeCl₃, FeSO₄ and the like. The examples of the preferable metaloxides to be further added are SiCl₄, ZrOCl₂, SnCl₄, Na₂O, SiO₂.5H₂O,MnCl₂, MgCl₂, AlCl₃ and the like. Acidity of the dispersion in thecourse of adding the precursors is retained preferably at pH 1 to 4.Acid, preferably hydrochloric acid is added to the dispersion to adjustpH between 1 and 4, and a basic aqueous solution such as sodiumhydroxide is added thereto so that the hydrous titanium dioxide or ironoxide may be adsorbed on the base material by introduction of metaloxides precursors. In this process, it is important to titrate theprecursors of metal oxides while maintaining said pH range. When pH ofthe dispersion is less than 1, a hydrolysis is not taken place, and whenpH of the dispersion exceed 4, a hydrolysis is rapidly taken place andthereby causing the metal oxides not to be coated on the base materialand to be agglomerated each other. This coating method is well known bythe skilled in the art. Generally, a coating layer having anatasecrystal structure is formed when the coating layer of the hydrous metaloxide is formed on the synthesized mica as a base material, however, acoating layer having rutile crystal structure may be formed byprecoating the synthesized mica with tin dioxide (SnO₂) layer asdisclosed above. As the titration of the precursors proceeds, thecoating thickness of the hydrous metal oxide increases. The colors ofsilver, gold, red, purple, blue and green exhibit in proportion to thethickness. The synthesized mica coated as above is subjected tofiltration, washing with water, drying, calcination, and screening tomake final product in a mass production. The above processes after thecoating process is well known in the art.

[0039] In the mean time, the present invention provides a pearlescentpigment prepared by adding a suitable surfactant prior to the coatingprocess of metal oxide. Submicron-sized particles attached to the largeparticles or overlapped each other are dispersed on account of repellingforce at the electrically charged interfaces of the synthesized mica byadding the surfactant, thereby the pigment particles are prevented frombeing agglomerated each other. Further, the interface of the synthesizedmica and the interface of the hydrous metal oxide adsorbed to the basematerial by the hydrolysis are activated to allow smooth and stableadsorption. Particularly, when the hydrous metal oxides are not adsorbedon the base material and agglomerated by themselves to form the freeparticles, luster deteriorates and the amount of the metal oxideprecursors is more needed than actually required. Accordingly, theamount of the generated waste can be reduced and the cost for preparingthe pigment can be reduced by using a surfactant. The surfactant used inthe present invention is selected from cationic, anionic, nonionic oramphionic surfactants. Examples of the anionic surfactant include sodiumbistridecyl sulfosuccinate, sodium diisopropyl naphthalene sulfonate andthe like. Examples of the cationic surfactant includealkylamine-guanidine polyoxyethanol, etc. Examples of the nonionicsurfactant include sorbitan monooleate, etc. Examples of amphionicsurfactant include cocoamidopropyl betaine, etc. The surfactant whichcan be used in the present invention is not limited to the above listedones, various surfactants can be used as long as the present inventioncan be attained. Such use of the surfactant is advantageous in that thesynthesized mica particles ground by a water mixer as well as theconventional wet pulverizer can be used. 0.0001 to 1.0% by weight of thesurfactant is added to the dispersion of the synthesized mica, retainedfor 10 to 20 minutes, and then subjected to the coating process of themetal oxide.

[0040] The present invention is described in more detail by Examples andComparative Examples, but the Examples are only illustrative and,therefore, not intended to limit the scope of the present invention.

EXAMPLE 1

[0041] The synthesized mica (JED-1 manufactured by Jiafeng Co., Ltd.)was ground in a water mixer and then separated to three portions asaverage sizes, 100 μm, 150 μm and 250 μm of the synthesized micaparticles. 100 g of the synthesized mica particles were added to anddispersed in 1 liter of the deionized water, and then raised to thetemperature of 60 to 100° C. Thereafter, 5% hydrochloric acid was addedthereto to lower pH to 1 to 3, and refluxed for 10 minutes. 40% TiOCl₂aqueous solution (a state TiCl₄ is soluted in water) was titrated andcontinued to maintain said pH with sodium hydroxide. As the amount ofTiOCl₂ to be added is increased, the colors of silver, gold, red, blueand green was exhibited, titration of TiOCl₂ was stopped upon obtainingthe desired color, refluxed for 10 minutes, and said solution wassubjected to filtration, washing and drying, and then calcined in anelectric furnace at the temperature of 700 to 1000° C. As a result ofX-ray diffraction analysis for the calcined pigment, it was confirmedthat titanium dioxide layer having anatase structure was formed on thesurface of the synthesized mica.

EXAMPLE 2

[0042] The synthesized mica used in Example 1 was ground in a watermixer and then separated to three portions as average sizes, 100 μm, 150μm and 250 μm of the synthesized mica particles. 100 g of thesynthesized mica particles were added to and dispersed in 1 liter of thedeionized water, and then raised to the temperature of 60 to 100° C.Thereafter, 5% hydrochloric acid was added thereto to lower pH to 1 to3, and refluxed for 10 minutes. 10 to 100 cc of 5% SnCl₄.n(H₂O) wereadded thereto and then refluxed for 10 minutes. 40% TiOCl₂ aqueoussolution was titrated and continued to maintain said pH with sodiumhydroxide. Titration of TiOCl₂ was stopped upon obtaining the desiredcolor, refluxed for 10 minutes, and said solution was subjected tofiltration, washing and drying, and then calcined in an electric furnaceat the temperature of 700 to 1000° C. As a result of X-ray diffractionanalysis for the calcined pigment, it was confirmed that titaniumdioxide layer having a rutile structure was formed on the surface of thesynthesized mica.

EXAMPLE 3

[0043] The same procedure as in Example 1 was carried out except that0.0001 to 1% by weight of OS (sodium diisopropyl naphthalene sulfonate,manufactured by Cytec. Co., Ltd.) as an anionic surfactant was addedbefore titrating 40% TiOCl₂ aqueous solution to obtain the pearlescentpigment. It was confirmed that the synthesized mica particles coatedwith titanium dioxide layer were not agglomerated each other anduniformly dispersed in the obtained pigment, and that the titaniumdioxide layer was smoothly and uniformly formed on the surface of thebase material.

EXAMPLE 4

[0044] The same procedure as in Example 1 was carried out except that0.0001 to 1% by weight of C-61 (alkylamine-guanidine polyoxyethanol,manufactured by Cytec. Co., Ltd.) as an anionic surfactant was addedbefore titrating 40% TiOCl₂ aqueous solution to obtain the pearlescentpigment. As is apparent in FIG. 2, it was confirmed that the synthesizedmica particles coated with titanium dioxide layer were not agglomeratedeach other and uniformly dispersed in the obtained pigment, and that thetitanium dioxide layer was smoothly and uniformly formed on the surfaceof the base material.

EXAMPLE 5

[0045] The same procedure as in Example 1 was carried out except that0.0001 to 1% by weight of TR 70 (sodium bistridecyl sulfosuccinate,manufactured by Cytec. Co., Ltd.) as an anionic surfactant was addedbefore titrating 40% TiCCl₂ aqueous solution to obtain the pearlescentpigment. It was confirmed that the synthesized mica particles coatedwith titanium dioxide layer were not agglomerated each other anduniformly dispersed in the obtained pigment, and that the titaniumdioxide layer was smoothly and uniformly formed on the surface of thebase material.

EXAMPLE 6

[0046] The same procedure as in Example 1 was carried out except that0.0001 to 1% by weight of Monopol SP-1 (Sorbitan monooleate,manufactured by Dong Nam Synthesis. Co., Ltd.) as an anionic surfactantwas added before titrating 40% TiOCl₂ aqueous solution to obtain thepearlescent pigment. It was confirmed that the synthesized micaparticles coated with titanium dioxide layer were not agglomerated eachother and uniformly dispersed in the obtained pigment, and that thetitanium dioxide layer was smoothly and uniformly formed on the surfaceof the base material.

EXAMPLE 7

[0047] The same procedure as in Example 1 was carried out except that0.0001 to 1% by weight of MITAINE CA (cocoamidopropyl betaine,manufactured by Cytec. Co., Ltd.) as an anionic surfactant was addedbefore titrating 40% TiOCl₂ aqueous solution to obtain the pearlescentpigment. It was confirmed that the synthesized mica particles coatedwith titanium dioxide layer were not agglomerated each other anduniformly dispersed in the obtained pigment, and that the titaniumdioxide layer was smoothly and uniformly formed on the surface of thebase material.

EXAMPLE 8

[0048] The synthesized mica used in Example 1 was ground in aconventional wet pulverizer and then separated to average size 20 μm ofthe synthesized mica particles. 80 g of the synthesized mica particleswere dispersed in 1 liter of deionized water, raised to the temperatureof 60 to 100° C., and then 0.0001 to 1% by weight of TR 70 (sodiumbistridecyl sulfosuccinate, manufactured by Cytec. Co., Ltd.) as ananionic surfactant was added thereto. Thereafter, 5% hydrochloric acidwas added thereto to lower pH to 1 to 3, and refluxed for 10 minutes. 10to 100 cc of 5% SnCl₄.n(H₂O) were added to the dispersion and thenrefluxed for 10 minutes. 40% TiOCl₂ aqueous solution was titrated andcontinued to maintain said pH with sodium hydroxide. Titration of TiOCl₂was stopped upon obtaining the desired color, refluxed for 10 minutes,and said solution was subjected to filtration, washing and drying, andthen calcined in an electric furnace at the temperature of 700 to 1000°C. As a result of X-ray diffraction analysis for the calcined pigment,it was confirmed that titanium dioxide layer having rutile structure wasformed on the surface of the synthesized mica.

EXAMPLE 9

[0049] The same procedure as in Example 1 was carried out except thatthe synthesized mica ground in a water mixer was further pulverized inan edge runner mill, and separated to five portions as average particlesizes, 8 μm, 10 μm, 200 μm, 50 μm and 80 μm, of the synthesized micaparticles, and the obtained particles were coated with titanium dioxidelayer. As a result of X-ray diffraction analysis for the calcinedpigment, it was confirmed that titanium dioxide layer having anatasestructure was formed on the surface of the synthesized mica and thatluster was highly improved on account of more minute particles.

EXAMPLE 10

[0050] The same procedure as in Example 2 was carried out except thatthe synthesized mica ground in a water mixer was further pulverized inan edge runner mill, and then separated to five portions as averageparticle sizes, 8 μm, 10 μm, 200 μm, 50 μm and 80 μm of the synthesizedmica particles, and the obtained particles were coated with titaniumdioxide layer. As a result of X-ray diffraction analysis for thecalcined pigment, it was confirmed that titanium dioxide layer havingrutile structure was formed on the surface of the synthesized mica andthat luster was highly improved on account of more minute particles.

EXAMPLE 11

[0051] The same procedure as in Example 3 was carried out except thatthe synthesized mica ground in a water mixer was further pulverized inan edge runner mill, and then separated to five portions as averageparticle sizes, 80 μm, 10 μm, 20 μm, 50 μm and 80 μm of the synthesizedmica particles, and the obtained particles were coated with titaniumdioxide layer. As a result of X-ray diffraction analysis for thecalcined pigment, it was confirmed that titanium dioxide layer havinganatase structure was formed on the surface of the synthesized mica andthat the dispersibility among the particles was highly improved, andthus luster was excellent.

EXAMPLE 12

[0052] The same procedure as in Example 4 was carried out except thatthe synthesized mica ground in a water mixer was further pulverized inan edge runner mill, and then separated to five portions as averageparticle sizes, 80 μm, 10 μm, 20 μm, 50 μm and 80 μm of the synthesizedmica particles, and the obtained particles were coated with titaniumdioxide layer. As a result of X-ray diffraction analysis for thecalcined pigment, it was confirmed that titanium dioxide layer havingrutile structure was formed on the surface of the synthesized mica andthat the dispersibility among the particles was highly improved, andthus luster was excellent.

COMPARATIVE EXAMPLE 1

[0053] The same procedure as in Example 1 was carried out except thatthe synthesized mica “JED-1” (manufactured by Jiafeng Co., Ltd.) wasground in an edge runner mill and then separated to three portions asaverage particle sizes, 100 μm, 150 μm and 250 μm of the synthesizedmica to obtain pearlescent pigment. As is apparent in FIGS. 3 and 4, itwas confirmed that the synthesized mica particles in the obtainedpigments were agglomerated each other, and that the titanium dioxidelayer was not uniformly formed on the surface of the base material.

COMPARATIVE EXAMPLE 2

[0054] The same procedure as in Comparative Example 1 was carried outexcept that the synthesized mica particles having average particlesizes, 80 μm, 10 μm, 20 μm, 50 μm and 80 μm were obtained by using anedge runner mill, and then the particles were coated with titaniumdioxide layer to obtain pearlescent pigments. The obtained pigments werebetter in luster and chroma than those obtained in Comparative Example1, however the synthesized mica particles were slightly agglomeratedeach other, and the titanium dioxide layer was not satisfactory inflatness.

EXAMPLE 13 Evaluation of Luster and Chroma

[0055] The luster and chroma of the pearlescent pigments prepared inExamples 1 to 4 and Comparative Example 1 were evaluated as follows andthe results were shown in Table 1, below. The evaluation was commencedby mixing a nitrocellulose solution having a viscosity of 1,200 cps witha pearlescent pigment (weight ratio of 94:6) by using a mixing bar,letting a certain amount of the mixture fall on a draw down card (D.Dcard) at the same place as ST sample, drawing down the mixture from theabove-obtained card onto a concealing rate measure paper printed withblack and white colors by use of a doctor blade, and drying it in theair. The luster and chroma were evaluated with naked eyes. TABLE 1 Comp.Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Luster ⊚ ⊚ ⊚ ⊚ Δ Chroma ⊚ ⊚ ⊚ ⊚ Δ

EXAMPLE 14 Evaluation of Luster and Chroma

[0056] The luster and chroma of the pearlescent pigments prepared inExamples 8 to 12 and Comparative Example 2 were evaluated as follows andthe results were shown in Table 2, below. The evaluation was commencedby mixing a nitrocellulose solution having a viscosity of 1,200 cps witha pearlescent pigment (weight ratio of 94:6) by using a mixing bar,letting a certain amount of the mixture fall on a draw down card (D.Dcard) at the same place as ST sample, drawing down the mixture from theabove-obtained card onto a concealing rate measure paper printed withblack and white colors by use of a doctor blade, and then drying it inthe air. The luster and chroma were evaluated with naked eyes. TABLE 2Comp. Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 2 Luster ⊚ ⊚ ⊚ ⊚ ⊚ ◯ Chroma ⊚⊚ ⊚ ⊚ ⊚ ◯

EXAMPLE 15 Evaluation on Surfactant's Effect

[0057] The luster, chroma and dispersibility of the pearlescent pigmentsprepared in Examples 3 to 7 and Comparative Example 1 were evaluated asfollows. The luster and chroma of the pearlescent pigment were evaluatedin a same manner as Examples 13 and 14, and the dispersibility of thepearlescent pigment was evaluated by comprehensively considering luster,chroma, shielding property and the like. The results were shown in Table3, below. TABLE 3 Comp. Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 1 Luster ⊙ ⊙ ⊙⊙ ⊙ ◯ Chroma ⊙ ⊙ ⊙ ⊙ ⊙ ◯ Dispersibility ⊙ ⊙ ⊙ ⊙ ⊙ ◯

Industrial Applicability

[0058] According to the present invention, the synthesized mica as basematerial is ground in a water mixer to make the obtained particlessmooth, to uniformly and smoothly coat metal oxides, and thus to obtainthe pearlescent pigment having excellent luster and chroma. Further, thesurfactant may be added to the synthesized mica ground by using a watermixer and/or a conventional wet pulverizer, and the obtained synthesizedmica may be coated with metal oxides, and thereby attaining an excellentdispersibility of the particles and smooth coating layer.

[0059] The present invention being thus described, it will be obviousthat the same may be varied in many ways. Such variations are not to beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A method for preparing a pearlescent pigment bycoating metal oxides on the synthesized mica, comprising the steps of:(1) grinding the synthesized mica by agitating the mica with water in awater mixer to a particle size between 100 and 500 μm and separating themica; (2) dispersing the separated particles of the synthesized mica inwater and adding acid thereto to adjust pH between 1 and 4; (3) addingthe metal oxide precursors and the basic aqueous solution to thedispersion while maintaining said pH range until the desired color isattained, and thereby forming at least one hydrous metal oxides layerson the particles of the synthesized mica; and (4) filtering,water-washing, drying and calcining the synthesized mica coated with themetal oxides layers.
 2. A method for preparing a pearlescent pigment bycoating metal oxides on the synthesized mica, comprising the steps of:(1) grinding the synthesized mica by agitating the mica with water in awet pulverizer to a particle size between 5 and 500 μm and separatingthe mica; (2) dispersing the separated particles of the synthesized micain water and adding 0.0001 to 1.0% by weight of cationic, anionic,nonionic or amphionic surfactant thereto; (3) adding acid to thedispersion containing the surfactant to adjust pH between 1 and 4; (4)adding the metal oxide precursors and the basic aqueous solution theretowhile maintaining said pH range until the desired color is attained, andthereby forming at least one hydrous metal oxides layers on theparticles of the synthesized mica; and (5) filtering, water-washing,drying and calcining the synthesized mica coated with the metal oxideslayers.
 3. The method for preparing a pearlescent pigment as set forthin claim 1 or 2, wherein the metal oxide layer comprises one or morethan two metal oxides.
 4. The method for preparing a pearlescent pigmentas set forth in claim 3, wherein the metal oxide layer is titaniumdioxide (TiO₂) layer, iron oxide (Fe₂O₃) layer, or the combinationthereof.
 5. The method for preparing a pearlescent pigment as set forthin claim 3, wherein the metal oxide layer comprises a main metal oxidecomponent and an assistant metal oxide component, the main metal oxidecomponent being selected from the group consisting of titanium dioxide(TiO₂), iron oxide (Fe₂O₃) and a mixture thereof, and the assistantmetal oxide component being selected from the group consisting of tindioxide (SnO₂), zirconium dioxide (ZrO₂), silicon dioxide (SiO₂),aluminum oxide (Al₂O₃), magnesium oxide (MgO), manganese dioxide (MnO₂)and a mixture thereof.
 6. The method for preparing a pearlescent pigmentas set forth in claim 1, further comprising a step of re-coating thecalcined pigment particles with a metal oxide selected from the groupconsisting of chromium, zirconium, aluminum and a mixture thereof ortreated with silane.
 7. The method for preparing a pearlescent pigmentas set forth in claim 1, further comprising a step of adding 0.0001 to1.0% by weight of the cationic, anionic, nonionic or amphionicsurfactant to the dispersion of the synthesized mica.
 8. The method forpreparing a pearlescent pigment as set forth in claim 2 or 7, whereinthe anionic surfactant is sodium bistridecyl sulfosuccinate or sodiumdiisopropyl naphthalene sulfonate; the cationic surfactant isalkylamine-guanidine polyoxyethanol; the nonionic surfactant is sorbitanmonooleate; and the amphionic surfactant is cocoamidopropyl betaine. 9.The method for preparing a pearlescent pigment as set forth claim 1,wherein the grinding step of the synthesized mica is carried out byintroducing water and the synthesized mica in the water mixer at aweight ratio of 10:1 to 1:1, and agitating them at the revolution speedof 100 to 1000 rpm for 0.5 to 2 hours.
 10. The method for preparing apearlescent pigment as set forth in claim 1, further comprising a stepof pulverizing the particles of the synthesized mica to a size of 5 to100 μm with a wet pulverizer after grinding the synthesized mica withthe water mixer.
 11. A pearlescent pigment prepared in accordance withclaim 1 or 2.